A portion of the disclosure including microfiche Appendix A of this patent document contains material which is subject to copyright protection. The copyright or owner has no objection to the facsimile reproduction by any-one of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all (copyright or mask work) rights whatsoever.
The present application includes a computer listing on microfiche Appendix A attached hereto. Microfiche Appendix A includes frames 1-178 disposed on 2 sheets.
The present invention relates generally to radio frequency (RF) communication systems. More particularly, the present invention relates to channel searching techniques for radio transceivers.
Radio systems are utilized in diverse applications to provide a variety of communication operations. Radio systems, such as, the commercial high-frequency (HF) data link radio, can be used to support air traffic control (ATC) and airline operational control (AOC). The HF data link radio can be used to transmit and receive voice, tactical, data, and navigational messages between aircraft and ground stations.
Radios or transceivers generally communicate messages on a channel of a communication link in accordance with a protocol associated with the communication link. For example, commercial HF data link radios or transceivers transmit and receive messages on one of about 400 channels in the frequency range between 2-30 Megahertz (MHZ). Each channel has a bandwidth of approximately 1800 bytes per second.
Commercial HF data link radios communicate ATC and AOC messages in accordance with a time division multiplexing scheme, such as, the time division multiplex access (TDMA) protocol defined in Aeronautical Radio, Inc. (Air Inc.) specification 635. The TDMA protocol allows several radios to use a single channel without interference from each other.
Conventional radio systems establish contact or connections on a channel in accordance with the protocol associated with the data link. The radio system is tuned to the appropriate channel and transmits and receives messages in accordance with the protocol. According to the commercial HF data link radio example, the airborne radio system establishes contact or connects to a base station on a particular HF frequency (e.g., channel). The radio system connects or logs on by receiving a squitter message on a particular channel and transmits information in accordance with the squitter message on the particular channel.
The particular channel (e.g., the main channel) is selected by the HF Data Link frequency search algorithm in accordance with the signal-to-noise ratios that have been experienced on the received frequencies. The HF data link frequency search algorithm attempts to choose a robust channel that will be available for the entire communication session with a ground station. Nonetheless, radio systems can have contact broken or lose the connection due to a variety of internal and external conditions. For example, an aircraft utilizing HF data link may lose contact at any time due to operational conditions of the radio system, geographic conditions (e.g., mountains and valleys), distance, weather, solar conditions, and other external situations. In radio systems, particularly HF data link radio systems utilized in aircraft applications, the amount of time during which the radio system is incapable of communicating (e.g., lost contact time) should be minimized.
In conventional voice HF operations, when the radio system loses connectivity, the radio operator must search for another channel. The search can be augmented by various products and techniques which can help the radio operator predict the availability of alternative channels (channels other than the main channel, which is no longer operational). Additionally, the skill and experience of the radio operator are extremely important when determining the availability of alternate channels. Even with a highly skilled radio operator, the time spent searching for alternate channels adversely affects the operation of the radio system. In fact, search times for alternative channels can be as long as several minutes. Once a suitable alternative channel is found, connectivity is reestablished on the alternate channel, which then becomes the main channel.
Thus, there is a need for a radio system that reduces search time associated with selecting alternate channels. Further still, there is a need for an automatic channel search algorithm that can automatically select a channel for HF data link operations, and make a list of best available alternate channels for human-operator use. Further still, there is a need for a channel selection algorithm that does not affect communication on the main channel.
The present application relates to a transceiver apparatus for use with a high frequency (HF) radio communication system. The communication system includes a plurality of channels. The transceiver apparatus communicates information on a selected channel of the channels. The transceiver apparatus determines the actual availablity of at least one different channel of the channels. The transceiver apparatus displays visual indicia of the actual availability of the at least one different channel.
The present invention further relates to a radio capable of receiving radio signals on an HF data link. The radio signals are communicated on at least a first channel, a second channel and a third channel. The radio signals are communicated in accordance with a time division multiplex protocol including a plurality of time slots. A first squitter message is provided on the first channel in a first time slot, and a second squitter message is provided on the second channel in a second time slot. A third squitter message is provided on the third channel in a third time slot. The radio includes control means for monitoring actual availability of at least the second channel in response to the second squitter message while communicating information on the first channel in accordance with the time division multiplex protocol. The radio also includes display means for displaying an indicia of at least the second channel based upon the actual availability of the second channel.
The present invention still further relates to a method of determining availability of alternative channels on an HF link. The method includes communicating in at least one assigned time slot on a main channel, determining the actual availability of the at least one alternative channel, and providing an indication of the actual availability.